1. Field of the Invention
The present invention relates to an antenna apparatus used for receiving an electric wave and more particularly, to a portable antenna apparatus having a collapsible loop-shaped antenna element.
2. Description of the Prior Art
A signal receiving apparatus such as a radio receiver for receiving a radio broadcast has an antenna apparatus for receiving a broadcast electric wave. As an antenna apparatus of this type, there can be exemplified a rod antenna apparatus constituted by a plurality of rod-shaped antenna members connected to one another so as to be extended and contracted as a whole, and a loop antenna apparatus having a reception surface defined by a linear antenna element formed in a single loop shape.
A portable radio receiver normally has a rod antenna apparatus which can be contained unitarily with the receiver main body, in order to promote easiness for carrying. The rod antenna apparatus has a plurality of rod-shaped antenna elements which are connected in such a manner that they can be extended and contracted as a whole. When not in use, they are contracted so as to be contained in the apparatus main body for easiness of carrying the radio receiver. The rod type antenna apparatus provided in a radio receiver is extended when receiving a radio broadcast so that a broadcast electric wave can be advantageously received.
As in the rod antenna apparatus, a plurality of antenna elements are extended in when the straight line, the antenna may readily collide with something while carrying the radio receiver. When subjected to a shock by collision, the rod antenna apparatus formed by a plurality of antenna elements of thin rod shape connected to each other is easily bent and further may be broken in the middle.
On the other hand, the loop antenna can improve the reception sensitivity in proportion to the reception area surrounded by the antenna element curved into an almost loop shape. However, if the loop diameter of the antenna element is increased so as to increase the reception sensitivity, the antenna cannot be used as a portable type radio receiver.